U.S. patent number 5,023,097 [Application Number 07/352,771] was granted by the patent office on 1991-06-11 for delignification of non-woody biomass.
This patent grant is currently assigned to Xylan, Inc.. Invention is credited to George J. Tyson.
United States Patent |
5,023,097 |
Tyson |
* June 11, 1991 |
Delignification of non-woody biomass
Abstract
A non-woody biomass is delignified through extrusion technology,
utilizing hydrogen peroxide and an alkali agent, to break down
complex biomass materials. The process is useful in forming a
highly absorbant fiber material for use as a dietary fiber or an
absorbant fiber. Alternatively, the process is useful for preparing
dietary feeds for ruminant animals, as well as produce a broad
range of alcohols or polymers from the non-woody lignocellulosic
substrate.
Inventors: |
Tyson; George J. (Madison,
WI) |
Assignee: |
Xylan, Inc. (Madison,
WI)
|
[*] Notice: |
The portion of the term of this patent
subsequent to June 27, 2006 has been disclaimed. |
Family
ID: |
26873647 |
Appl.
No.: |
07/352,771 |
Filed: |
May 16, 1989 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
177786 |
Apr 15, 1988 |
4842877 |
Jun 27, 1989 |
|
|
Current U.S.
Class: |
426/271; 127/37;
426/443; 426/615; 426/804; 426/807 |
Current CPC
Class: |
A61L
15/28 (20130101); A61L 15/40 (20130101); C05F
11/00 (20130101); D21C 3/02 (20130101); D21C
3/24 (20130101); A61L 15/28 (20130101); C08L
1/02 (20130101); A23K 10/32 (20160501); A23K
10/30 (20160501); A23K 50/10 (20160501); A23L
33/21 (20160801); Y10S 426/804 (20130101); Y10S
426/807 (20130101) |
Current International
Class: |
A23K
1/00 (20060101); A23K 1/12 (20060101); A23K
1/14 (20060101); A23K 1/18 (20060101); A23L
1/308 (20060101); A61L 15/40 (20060101); A61L
15/28 (20060101); A61L 15/16 (20060101); C05F
11/00 (20060101); D21C 3/24 (20060101); D21C
3/02 (20060101); D21C 3/00 (20060101); A23K
001/00 () |
Field of
Search: |
;426/615,623,630,636,271,443,804,807,271 ;127/1,57,37 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Wenger advertisement, X-200 Continuous Extrusion Cooker, Bulletin
No. 31-3R84, 4 pages. .
Chementator article from Chemical Engineering, Mar. 14, 1988, p.
19. .
"There's New Life in Continuous Fermentation", Chemical Week, Feb.
22, 1984. .
Gould, J. Michael and S. N. Freer, High-Efficiency Ethanol
Production from Lignocellulosic Residues Pretreated with Alkaline
H.sub.2 O.sub.2, Biotech. and Bioengineering, Vol. XXVI, pp.
628-631 (1984). .
Easterbrook, Cregg, "A Feeding Machine", Science, Jan./Feb. 1986,
pp. 48-54. .
Potter, Anne Murielle, "Steak or Stake?", Bio-Joule, Sep. 1987, pp.
8-9..
|
Primary Examiner: Penland; R. B.
Attorney, Agent or Firm: Andrus, Sceales, Starke &
Sawall
Parent Case Text
This is a continuation of application Ser. No. 07/177,786, filed
04/05/88, now U.S. Pat. No. 4,842,877, issued June 27, 1989.
Claims
What is claimed is:
1. A process for continuously treating a non-woody ligno-cellulosic
substrate consisting of organic plant material having no more than
about 20% lignin content, the process consisting essentially
of:
a) reacting the substrate in a reaction medium including an aqueous
solution of a strong alkali at a pH in the range of about 10.5 and
12.5; and
b) continuously feeding the product of step a) to an aqueous
solution in a pressurized extruder reactor and reacting the
substrate in an oxygen atmosphere at a temperature between about
150.degree. and 315.degree. F. and at a pressure between about 250
and 450 psi, and in the presence of hydrogen peroxide for a period
of time effective to delignify the substrate, wherein the hydrogen
peroxide is added to the extruder at a rate of between about 20 and
40 pounds of hydrogen peroxide per ton of substrate.
2. The process of claim 1 wherein the substrate is selected from
the group comprising tree fruits, citrus fruits, bushberries,
cereal grains and agricultural residues.
3. The process of claim 1 wherein the substrate is reduced in size
to a particle not more than one-half inch in length prior to
reacting in the reaction medium.
4. The process of claim 1 wherein the substrate is reacted in a
reaction medium in a prehydrolysis tank, wherein the substrate is
softened in the reaction medium at a temperature between
130.degree. and 160.degree. F.
5. The process of claim 1 wherein the alkali is selected from the
group consisting of sodium hydroxide and potassium hydroxide.
6. The process according to claim 1 wherein the reaction medium is
removed from the substrate prior to feeding the substrate to a
pressurized extruder reactor.
7. The process of claim 1 wherein the substrate is reacted in the
extruder reactor at a pH between about 11.2 and about 11.8.
8. The process of claim 1 further comprising adding chelating
agents and buffering agents to the aqueous solution of the extruder
reactor.
9. A process for continuously preparing a nearly while, non-woody,
delignified dietary fiber suitable for food grade consumption,
wherein the fiber contains at least 80% cellulose, the process
consisting essentially of the following steps in sequence:
a) reacting an organic non-woody lignocellulosic substrate having
no more than about 20% lignin in a reaction medium including an
aqueous solution of a strong alkali at a pH in the range of about
10.5 and 11.8;
b) continuously feeding the substrate to an aqueous solution in a
pressurized extruder reactor and reacting the substrate in an
oxygen atmosphere at a temperature between about 150.degree. and
315.degree. F. and at a pressure between about 250 and 450 psi, and
in the presence of hydrogen peroxide for a period of time effective
to delignify the substrate wherein the hydrogen peroxide is added
to the extruder at a rate of between and 20 and 40 lbs. of hydrogen
peroxide per ton of substrate;
c) washing the substrate in an aqueous wash solution to remove the
hemicellulose and lignin from the substrate;
d) washing the substrate in an acid bath including an aqueous acid
bath solution having a pH between about 0.5 and 3.0;
e) washing the substrate in an aqueous pH correction solution,
wherein a buffering agent is added to the aqueous pH correction
solution to adjust the pH to between about 6.5 and 7.0;
f) reducing the moisture content of the substrate to a moisture
level between about 55% and 65%;
g) fluffing the substrate; and
h) drying the substrate at a temperature no greater than
180.degree. F.
10. The process of claim 9 wherein the substrate is selected from
the group comprising tre fruits, vegetables, citrus fruits,
bushberries, cereal grains and agricultural residues.
11. The process of claim 9 wherein the substrate is reacted in a
reaction medium in a prehydrolysis tank, wherein the substrate is
softened in the reaction medium at a temperature between
130.degree. and 160.degree. F.
12. The process of claim 9 further comprising removing the
hemicellulose and lignin from the substrate in an agitated water
tank at a temperature of at least 140.degree. F.
13. A process for continuously preparing a highly absorbent fiber
source consisting essentially of the following steps in
sequence:
a) reacting a non-woody lignocellulosic substrate consisting of
organic plant material having no more than about 20% lignin content
in a reaction medium including an aqueous solution of a strong
alkali at a pH in the range of about 10.5 and 12.5;
b) continuously feeding the substrate to an aqueous solution in a
pressurized extruder reactor in oxygen atmosphere at a temperature
between about 150.degree. and 315.degree. F. and at a pressure
between about 250 and 450 psi, and in the presence of hydrogen
peroxide for a period of time effective to delignify the substrate
wherein the hydrogen peroxide is added to the extruder at a rate of
between and 20 and 40 lbs. of hydrogen peroxide per ton of
substrate;
c) washing the substrate in an aqueous wash solution to remove the
hemicellulose and lignin from the substrate;
d) washing the substrate in an acid bath including an aqueous acid
bath solution having a pH between about 0.5 and 3.0;
e) washing the substrate in an aqueous pH correction solution,
wherein a buffering agent is added to the aqueous pH correction
solution to adjust the pH to between about 6.5 and 7.0;
f) reducing the moisture content of the substrate to a moisture
level between about 55% and 65%;
g) fluffing the substrate; and
h) drying the substrate at a temperature no greater than
180.degree. F.
Description
FIELD OF THE INVENTION
The present invention is directed to a process and apparatus for
the delignification of non-woody biomass through extrusion
technology to break down complex biomass materials. Specifically,
the present invention is directed to the delignification of
non-woody agricultural biomass wastes through extrusion technology,
utilizing hydrogen peroxide and an alkali. The invention is
particularly directed to the formation of specific chemicals and
dietary fiber for use in food products. The present invention is
also directed to a process and apparatus for preparing useful
dietary feeds for ruminant animals.
BACKGROUND OF THE INVENTION
DESCRIPTION OF THE PRIOR ART
The importance of dietary fiber for use in the human and non-human
system cannot be overemphasized. Dietary fiber plays a major role
in health and disease resistance, physiological metabolism, and in
preventative medicine. There has been considerable effort in the
development of fiber-containing foods in order to benefit from the
advantages of dietary fiber in the system.
Further, many of these materials can be used as an effective
carbohydrate and energy source in ruminant feeds. However, in order
to benefit from these advantages, the lignocellulosic materials in
the residues must be converted into materials which can be
metabolized by the animal. Specifically, the polysaccharide portion
of these agricultural residues have to be converted into monomeric
sugars.
In order to accomplish this, it is important to break down the
lignin in the residues to release the beneficial polysaccharides in
the plant cell wall.
Originally, the delignification process used sulfuric acid and
chlorine as the main agents. However, due to environmental control
process problems, sulfuric acid is now being replaced with sodium
hydroxide and oxygen.
As an example in woody fibers, U.S. Pat. No. 4,459,174 to
Papageorges, et al. discloses a process for the delignification and
bleaching of chemical and semi-chemical cellulosic pulps in which
the pulp is subjected to a treatment with oxygen and subsequent
treatment with peroxide. The effluent from the treatment with
peroxide is at least partially recycled to the treatment with
oxygen.
U.S. Pat. No. 4,451,332 to Annergren, et al. is directed to a
method for the delignification of lignocellulose containing fiber
material comprising mixing an oxygen-containing gas with the
cellulose fiber material in order to atomize the gas and form a
foam of the gas and the cellulose fiber material. This process
provides a bleached, delignified cellulose fiber without bleaching
the lignin substance extracted from the material.
U.S. Pat. No. 4,372,812 to Phillips, et al. is directed to a
chlorine-free bleaching process for lignocellulosic pulp. This
process is characterized by a series of bleaching stages comprising
in sequence a peroxide bleaching stage, and at least one ozone
bleaching stage.
U.S. Pat. No. 4,311,553 to Akerlund, et al. is directed to a method
of producing peroxide bleached pulp by impregnating lignocellulose
fiber material with an aqueous silicate solution containing a
sequestering agent. The fiber material is preheated with saturated
steam and defibrated between two grinding disks in an atmosphere of
saturated steam at a temperature of 100.degree.-170.degree. C.
U.S. Pat. No. 4,298,425 to Ranzen, et al. is directed to a method
and apparatus for producing fiber pulp of improved paper-forming
characteristics from lignocellulose-containing material such as
wood chips and the like.
U.S. Pat. No. 4,214,947 to Berger is directed to the treatment of a
cellulosic material in the form of wood chips to produce at least
partial delignification without mechanical grinding. The material
is brought into contact with a reagent, e.g., steam or a chemical
reagent, and is subjected to alternate increases and decreases in
pressure.
U.S. Pat. No. 4,187,141 to Ahrel is directed to a method of
producing mechanical pulp of improved brightness and
light-scattering properties from wood chips, which are ground
between a pair of disks. The chips are impregnated with a solution
of alkali and introduced into a pressure vessel which is in
communication with the grinding zone.
U.S. Pat. No. 4,444,621 to Lindahl is directed to a process and
apparatus for the deresination and brightness improvement of
cellulose pulp, by adding an alkali to the pulp, along with a
sufficient oxidizing bleaching agent.
While the above processes are mainly directed to the
delignification of woody-like materials, there are other processes
known to the art which disclose the delignification of non-woody
biomasses to produce food fit for human and animal consumption. For
example, U.S. Pat. No. 4,136,207 to Bender discloses a process for
the delignification and fractionation of non-woody substrates using
a reactor and acid hydrolysis. This process uses a pH of 1.5 as the
first step with heat and pressure and a residence time of 6-13
minutes. Hemicellulose is extracted from the residues, and the
residues are subjected to hydrolysis for further fermentation to
ethanol, butanol, acetic acid, furfural, and xylitol. The cellulose
and lignin are then treated with an alkaline solution and separated
for independent uses.
U.S. Pat. No. 4,649,113 to Gould discloses a batch process for the
delignification of agricultural residues to produce cattle feeds,
chemical feeds or dietary fibers through the separation of these
components. The agricultural crop residues and other non-woody
lignocellulosic plant substrates are treated with hydrogen peroxide
at a controlled pH within the range of about 11.2 to 11.8. The
substrates are partially delignified. This process does not use a
reactor or mechanical shear and compression device, but utilizes
pHs within the range of about 11.2 to 11.8 with hydrogen peroxide
in the liquid. The cell walls are fractured in approximately 4 to 6
hours. The product can be used for animal feeds. It is also
possible to separate the liquid from the cell walls if dietary
fiber as a product is desired.
While there are processes and apparatuses available which delignify
both woody and non-woody cellulosic materials, these processes have
inherent deficiencies. For example, with the process as disclosed
in the '113 patent to Gould, maximum delignification of biomass or
non-woody lignocellulosic materials is achieved by the use of
substantial amounts of hydrogen peroxide in an aqueous solution at
a pH of about 11.5 in stored tanks for 4 to 6 hours at temperatures
between approximately 50.degree. and 120.degree. F. With this
process, a substantial amount of chemicals must be utilized in
order to effect the required delignification of the fiber.
SUMMARY OF THE INVENTION
In accordance with this invention, it is an object to provide a
delignification process which permits the efficient utilization of
non-woody agricultural residues.
It is also an object of the present invention to provide a process
for the delignification of waste or very low value agricultural
biomass or industrial waste to produce value-added foods, solvents,
or polymers.
It is also an object of the present invention to provide a nontoxic
nutritional ruminant feed source at a cost less than traditional
energy foods.
It is also an object of the present invention to develop a process
which may produce a broad range of alcohols or polymers, such as
ethanol, butanol, butanediol, 2-3-L glycerol, acetic acid,
furfural, xylitol or single cell proteins.
It is also an object of the present invention to provide grain and
seed processors with a new use for their non-woody agricultural
residue waste hulls, shells or other waste portions of their
processing systems.
It is also an object of the present invention to produce a
non-toxic material which produces at least 80% cellulose in a food
grade dietary fiber that will be FDA approved.
These and other objects are met by the present invention which
discloses a method for continuously treating a non-woody
lignocellulosic substrate comprising reacting the substrate in a
reaction medium containing an aqueous solution of a strong alkali
at a pH in the range of about 10.5 and 12.5. This is followed by
adding a chelating agent to the substrate in an amount effective to
chelate the metal ions in the substrate. The substrate is then
continuously fed into a pressurized extruder reactor conducted in
an oxygen atmosphere at a temperature between about 150.degree. and
315.degree. F. and at a pressure between about 250 and 450 psi. The
reactor is operated in the presence of hydrogen peroxide, which is
added to the extruder at a rate of between about 20 to 40 pounds of
hydrogen peroxide per ton of substrate on a dry matter basis.
The process provides a mechanical extrusion system to mix, grind
and sterilize non-woody agricultural substrates while mixing them
with sodium hydroxide, potassium hydroxide or other buffering
agents in the presence of heat, pressure, and hydrogen peroxide.
Following the extruder reaction process, the substrate can be
passed to a cooling drum for bagging or truck loading, or passed
into enzyme and fermentation tanks for production of ethanol,
acetic acid or fermentation to 2, 3-butanediol or glycerol, or the
substrate can be further processed to produce a high quality
dietary fiber.
The process allows the mixture of grains, vegetables and fruits or
portions of these plants to be processed together, as well as
separately to achieve the proper proportions of non-digestible or
soluble dietary fiber.
Without wishing to be limited to one explanation, it is believed
that the process of the present invention disrupts the lignin and
cellulose comprising the essential part of the cell walls of the
plants allowing oxygen to escape. This happens as the bonds between
the hydrogen and oxygen erupt. The water and oxygen leave in the
form of steam. Hydrogen oxidizes and is eliminated as the pressure
is released and as the water hydrolizes hemicellulose, or other
polysaccharides, and lignin into the desired proportions to
customize the fiber, based on its usage. The biomass may be treated
with less hydrogen peroxide and correspondingly less alkali
buffering agents, such as sodium hydroxide or potassium hydroxide
in order to maintain an adjusted pH of approximately 11.5 and to
eliminate the need to handle and dispose of the liquid waste
stream.
The dietary food fiber may be produced from any of a number of
non-woody biomass sources by use of an extruder, by injecting
chemicals into the barrel, at specific points, to custom produce a
substrate which can then hydrolyzed and/or bleached and separated
into the ratios desired to meet the exacting specifications of the
baking and food preparation industry.
By the use of non-corrosive extruders, the substrates can be ground
and mixed utilizing less chemicals than the prior inventions. For
example, the process of the present invention is advantageous over
the '113 patent to Gould in that instead of 200 pounds of hydrogen
peroxide per ton of dry biomass, the process of the present
invention only requires between 20 and 40 pounds of hydrogen
peroxide and a corresponding lesser amount of sodium hydroxide or
other buffering agents for a ten-fold advantage in chemical cost to
give a superior delignification effect. The process is expected to
allow fermentation of, or digestion of, 85 to 90% of the sugars,
calories, xylose or glucose.
The process utilizes no harsh toxin forming acids and uses a
natural combination of chemicals which dissipate under heat and
pressures of approximately 280.degree. F. and up to 400 pounds of
pressure in less than two minutes. The resulting substrates contain
no inhibitors to prevent enzymes or yeast from fermenting the
cellulose and hemicellulose to energy for ruminant feed stocks or
for use as chemical feed stocks to produce chemicals such as
ethanol or acetic acid or butanediol.
Further, the treatment of the substrate under the conditions of the
present invention increases, in situ, the normal digestibility of
the material to nearly 90% on a dry matter basis.
Further still, the continuous process of the present invention
increases product recovery as opposed to a batch process which must
be shut down on occasion in order to recover the batch product.
Further still, the process of the present invention requires no
presoaking of the raw material for any period longer than the
pre-mix time at the front end of the extruder. The temperature
range in the extruder is also effective in sterilizing the biomass
substrate by killing all bacteria, such as salmonella.
The process of the present invention has several uses. First, as a
food processing plant, the present invention effectively processes
products that are generally discarded, such as hulls, skins, and
the pulp of vegetables, grains and fruits, into animal feeds,
dietary fibers, absorbent materials, or chemical feed stocks for
new industries.
Of major importance, the process of the present invention
effectively produces a very light colored dietary fiber from grain
hulls or vegetable matter, which can be so customized to alter the
soluble portions versus the insoluble. The process of the present
invention produces a high percentage dietary fiber in the form of a
non-toxic, non-woody, nearly white, fluffy, cellulose material that
can be ground to a 120 mesh particle size which is highly water
soluble and non-gritty to the taste. Grinding of this fiber can be
accomplished with about one-third of the horsepower that is
required by the same substrate prior to processing, due to lignin
removal. Further, there is considerably less wear on the
apparatus.
The dietary fiber produced from the present invention has been
found to contain only 24 calories per hundred grams and can be used
as an effective replacement or substitute for some of the
ingredients in foods such as mashed potatoes, cakes, pasta,
cookies, donuts, pancakes, breads, meat loaves, pizza, and gravies.
For example, dietary fiber produced by the present invention can be
substituted for up to 33% of the white flour in white bread and 40%
in cakes and cookies.
Further, the process of the present invention produces a highly
absorbent fiber of light manilla color for food additives or
pharmaceutical use.
Further still, the process of the present invention advantageously
produces a light, fluffy, water absorbent fiber for absorbing body
fluids in products such as baby diapers, sanitary napkins, linens
and kitty litter.
The process of the present invention also can be utilized to
produce a pre-processed compost for greenhouses or mushroom bed
material, which allows accelerated growth of any horticulture
species, and allows for rapid micelial growth in a sterile
environment with all nematodes or bacteria killed during the
process. The compost material can be bagged after cooling.
Further still, the process of the present invention can be utilized
as a portable waste-processing system used by the fruit or
vegetable industry in reducing its disposal costs in many
agricultural operations and turning otherwise costly waste products
into new sources of fermentable sugar strains for the production of
dietary fiber products, chemicals such as acetic acid and ethanol,
cattle feeds, and compost material.
Further objects, features and advantages of the invention will be
apparent from the following detailed description when taken in
conjunction with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a schematic plan view of the process of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The process is directed to a continuous treatment of biomass to
produce dietary fiber and other desirable products in a convenient
and efficient way. By the use of a pressurized extruder, the
non-woody biomass substrate can be conveniently converted into the
desirable product in a fast and efficient manner while
substantially reducing the amount of necessary chemicals used to
delignify the biomass products. For purposes of the present
invention, the term "non-woody" is meant to include organic plant
material comprising no more than about 20% lignin.
By the term non-woody lignocellulosic substrate or biomass, it is
meant that the present invention can treat any non-woody materials
including tree fruits, such as apples, apricots, cherries, peaches,
pears, and plums; citrus fruits such as lemon, lime, oranges and
grapefruits; and bushberries such as blackberries, raspberries,
strawberries, and blueberries. Further, cereal grains such as
barley, corn, oats, rice, rye, and wheat, as well as the waste
material left after the processing of these materials, can be used.
In other words, agricultural residues such as corn stalks, wheat
straw, prairie grass, hulls of grains and brans, etc., are within
the scope of the substrates utilized in the present invention.
Reference is now made to the drawing which illustrates in schematic
form the process of the present invention. The biomass substrate,
which is preferably chopped or reduced in size to particles not
more than one-half inch in length, is fed to a prehydrolysis tank
10 in order to soften and solubilize the biomass. The prehydrolysis
tank 10 includes a reaction medium comprising a strong alkali which
softens the biomass at a pH between 10.5 and 12.5 and a temperature
between 130.degree. and 160.degree. F. Preferably, the
prehydrolysis tank 10 is an agitator tank. The preferred alkali in
the reaction medium is either sodium hydroxide or potassium
hydroxide. In some cases it may be preferred to keep the levels of
sodium reduced, especially for food grade applications. Sodium
levels may be kept reduced by the use of potassium hydroxide
instead of sodium hydroxide. The levels of potassium hydroxide may
additionally be reduced by the hydrolyzation of the prehydrolysis
tank reaction medium in a subsequent phase and the recycling of a
portion of that effluent, containing potassium hydroxide, back to
prehydrolysis tank 10. This recycling process may be conducted as
many as 7 to 10 times before the buffer loses its effectiveness.
The biomass substrate is preferably allowed to remain in the
prehydrolysis tank 10 for a period of at least 20 minutes at
temperatures between about 130.degree. and 160.degree. F., which
time has been shown to be an effective time to produce a
sufficiently softened and solubilized biomass for the next step. If
desired, the temperature of the reaction medium may be reduced to
ambient temperature; however the reaction time will be
correspondingly increased.
After the biomass has been sufficiently processed in the
prehydrolysis tank 10, the substrate is passed through line 12 and
filtered via filter 20. The filter 20 may be any of a number of
filters known to the art for removing a reaction medium from a
substrate. A preferred filter is a vibrating screen filter. The
purpose of the filter 20 is to remove the reaction medium from the
prehydrolysis tank 10 for recycling, via line 22, back to the
prehydrolysis tank 10. If necessary, the solution which is recycled
back to the prehydrolysis tank 10 may be pH corrected by the
addition of sodium hydroxide or other buffering material via line
24 from storage container 26. Additionally, it may be necessary to
correct the temperature of the recycled solution to be within the
preferred 130.degree. to 160.degree. F. temperature prior to
entering the prehydrolysis tank 10. The reaction medium may be
continuously recycled back to the prehydrolysis tank 10 until the
liquid becomes too densely contaminated. The contaminated reaction
medium is then replaced with fresh medium.
After a sufficient amount of the solution from the prehydrolysis
tank 10 has been removed by means of the filter 20, the biomass
substrate is then transferred via line 28 to a mixer 30. The
purpose of the mixer 30 is to remoisten the substrate to a desired
moisture percentage, normally 30% to 50% moisture and to add a
sufficient amount, preferably between about 2.5% and 4% v/v, of a
chelating agent, such as sodium silicate, which will be effective
to chelate the metal ions in the solution and coat any metals in
the apparatus.
The addition of sodium silicate or other chelating agents is
necessary in order to prevent unwanted precipitation of insoluble
deposits, such as metals or metal ions. These insoluble deposits
may tend to form deposits on any of the downstream components of
the apparatus of the present invention. The subsequent peroxide
bleaching can then be carried out with fully satisfactory results.
The addition of a chelating agent to the substrate also ties up the
metal ions in the substrate and water preventing unnecessary
oxidation of the hydrogen peroxide by the metal contact. This in
turn reduces any premature oxidation of the hydrogen peroxide,
reduces the amount of hydrogen peroxide needed by at least 10 to
20% and helps in the bleaching process of the substrate which is
very important in producing near white cellulose useful for dietary
fibers or absorbency products. Additionally, the chelating agent
coats any knives or discs in the downstream extruder barrel to
avoid product burn on or adherence buildup on the surfaces.
The substrate from line 28 is generally processed through the mixer
30 for a time between approximately 2 and 5 minutes at a pressure
between approximately 300 to 400 psi and a temperature between
190.degree. and 280.degree. F. If necessary, sodium hydroxide or
other alkali chemicals may be added from the buffer solution
storage tank 26 via line 32 in order to adjust the pH to between
about 11.2 and 12.2. If the hemicellulose is to be retained as in
the case of dietary fiber preparation, the pH should be adjusted to
between 11.4 and 11.8. The chelating agent is added from the
storage tank 34 via line 36. The chelating agent can be added
concurrently with the buffering agent prior to leaving the mixer
30.
After a sufficient amount of chelating agent and buffering agent
have been added to the substrate, the substrate is then passed via
line 38 to the extruder reactor 40. The extruder reactor 40 allows
for the effective treatment of the substrate with hydrogen peroxide
at higher solids levels. This eliminates a substantial amount of
the necessary liquid stream and improves the recovery of
carbohydrate products as in the case of animal feeds. The effect of
friction and pressure in the extruder is to accelerate the reaction
and to reduce the amount of hydrogen peroxide used while
maintaining the pH of the substrate at levels between about 11.2
and about 12.2, preferably between 11.4 and 11.8. Ideally, the
extruder reactor will process approximately 6,000 lbs. of substrate
per hour continuously. The advantage to the use of an extruder
reactor is that it replaces steam cooking in a batch process thus
making the entire process more efficient.
The extruder reactor is formed of a stainless steel or other
noncorrosive material and is modified to cram feed chopped biomass
at a 40 to 50% moisture level into a compression chamber with water
containing a 4% solution of chelating agent. The solution is pH
modified with either the addition of sodium hydroxide, potassium
hydroxide, or other buffering agent. The reaction takes place
within approximately 1.5 to 5 minutes at a pressure of between
approximately 250 and 450 psi, preferably 300 and 400 psi, and a
temperature between approximately 150.degree. and 315.degree. F.,
preferably 190.degree. and 280.degree. F., and most preferably
215.degree. to 275.degree. F. Advantageously, the substrate passing
through the extruder 40 may be delignified with as little as 20 to
40 lbs., preferably 25 lbs. of hydrogen peroxide per ton of
substrate on a dry matter basis.
Although the extruder reactor may be of twin-screw variety, it is
preferably a single screw stainless steel barrel with a steam
jacket, capable of food grade operation. The orifice is
hydraulically operated to control the temperature and time of the
process. Preferred extruders for purposes of the present invention
are the Wenger TX-138, X-175, X-185 or X-200 continuous extrusion
cookers, which operate at 150-250 horsepower for high capacity
industrial applications. These extruders have a feeder device which
provides a uniform and controllable feed rate to the extruder.
Pressure gauges are strategically placed to indicate pressure and
heat of the substrate throughout the extruder process. As indicated
above, the material of the reactor should be stainless steel or a
similar corrosion- free material. The reactor may be driven with a
variable speed or similar-type speed reduction motor. It will
become apparent from the following description of the extruder that
the extruder 40 will need several port entries to allow high
pressure pumps to introduce water in alkaline form, hydrogen
peroxide, sodium silicate or other chelating agent at any point
desirable in the process.
The pH of the extruder 40 should be maintained at between 11.2 to
11.8 if hemicellulose is to be retained. If the pH exceeds 11.8,
degeneration of the hemicellulose will be enhanced to a point where
almost all of the hemicellulose is reduced by hydrolyzation.
Therefore, the solubility of the fiber will be reduced. If the
hemicellulose retention is desired, the pH must be kept as near to
11.4 as possible. PH monitoring devices will be incorporated into
the reactor and subsequent hydrolyzing tanks. Preferably, they will
be computerized in order to control the level of operation of the
extruder 40.
In operation, the extruder is preferably equipped with a cram
feeder to forcefeed the biomass substrate into the throat of the
extruder barrel. During the extrusion process, sodium silicate or
other chelating agents may be injected, along with buffering
agents, oxygen or a suitable gas, and hydrogen peroxide. The
biomass enters the extruder 40 as a 35-45% solid substrate.
Oxygen is added to the extruder from an oxygen producing unit 42
via line 44. Oxygen is induced into the extruder in order to help
reduce the amount of hydrogen peroxide needed to cause a
delignification reaction on the cell walls. Further, the addition
of oxygen aids in the initiation and acceleration of the activation
of the hydrogen peroxide. A preferred oxygen producing tank is a
Prism.RTM. Alpha-Controlled Atmosphere System. The purpose of the
Prism.RTM. alpha-system is to generate nitrogen in order to extend
the storage life of food products. However, a biproduct of the
system is oxygen which is used in the present invention. Of course,
other oxygen producing systems may be incorporated into the process
of the present invention.
Following the introduction of oxygen, hydrogen peroxide from
storage tank 46 is added via line 48. Hydrogen peroxide causes a
reaction on the cell walls to allow the hemicellulose and lignin to
solubilize and be removed through a subsequent hydrolyzing process.
Approximately 20 to 40 lbs. of hydrogen peroxide is all that is
necessary to effectively process a ton of substrate through the
extruder 40. The hydrogen peroxide is injected approximately 1/3 of
the way into the reactor 40 system following the introduction of
oxygen. Hydrogen peroxide is generally diluted to a 10% or less
concentration to prevent accidents in transfer. Adequate moisture
is needed during this process to prevent too much heat from forming
which will cause charring of the material. The induction port 49
for the hydrogen peroxide may be adjusted so that most of the
hydrogen peroxide has decomposed by the time the biomass emerges
from the reactor 40. The hydrogen peroxide stream preferably passes
through a precious metal gauze screen under pressure to immediately
initiate the activation of the hydrogen peroxide. Preferred
precious metals include platinum and palladium with palladium being
most preferred.
It is a substantial benefit of the present invention that the
amount of hydrogen peroxide used in the present invention has been
reduced from other prior art processes. The reasons for this are
several. First, the material is processed in the extruder 40 under
elevated temperatures and pressure. Additionally, the material is
prevented from contacting surfaces with a sequestering agent, which
would cause the premature degeneration of the hydrogen peroxide.
Further still, all exposed surfaces of the components of the
present invention are of stainless steel or other noncorrosive
material.
Advantageously, all hydrogen peroxide is dissipated from the sample
collected within 24 hours of the treatment. This is important as
levels allowable under FDA will at all times need to be below 3 ppm
for GRAS affirmation. Human usage is especially important when it
comes to these levels.
The extruder 40 itself may be divided into as many as eight
sections, each of which being separated by a steam lock. The first
section, or cram feeder is designed to grab and feed the material
into the compression zones. This section operates at a speed of 300
RPM with a single screw against a shear block to pressurize. The
next section is designed to reabsorb the oxidizing agent, hydrogen
peroxide, that has been catalyzed by the metal acetate half way
down the reactor. This allows a necessary time for the oxidation
process to occur. The final section is an ancular die which extends
2 to 3 inches past the last steam lock.
A preferred extruder reactor includes a single screw stainless
steel barrel approximately 5 inches to 16 inches, preferably 5
inches to 51/2 inches, in diameter and 6 to 8 feet in length. The
extruder barrel should be made of a high carbon alloy or stainless
steel and having the strength to withstand pressures up to 500 psi
and temperatures exceeding 260.degree. F. A typical power source
for the extruder is a 200 horsepower, 3-phase electric motor
located near the entrance of the extruder. A 6:1 gear reducer
reduces the 1800 RPM drive to a 300 RPM extruder speed. A cram
feeder hopper powered by a variable speed hydraulic motor feeds the
materials, which may have a variable consistency, into the throat
of the extruder barrel. A second hopper or mixing pump combines a
diluted solution of an alkali agent, such as sodium hydroxide or
potassium hydroxide, into the substrate mass in the extruder
barrel. Hydrogen peroxide, in diluted form is then injected into
the substrate. The developing vapors are withdrawn by exhaust fans.
The process material is then augered either to a cooling drum for
bagging, to an enzyme or fermentation tank, or to an acid bath for
further processing to a dietary or absorbent fiber. Remotely
located safety sensing devices register both temperature and
pressure at the highest point in the extruder barrel. Both manual
and automatic shutdown devices are located throughout the system.
As a safety measure, a shroud, generally formed of stainless steel,
surrounds the extruder. The shroud includes devices which
continuously moniter the toxicity level of the emitted vapors. This
safety aspect of the system is able to signal and/or shut down the
machine without closing off the vapor exhaustion system until the
toxicity level is brought under control.
The biomass leaving the extruder should have a moisture level
between approximately 30 and 50%, preferably 40% moisture. The
temperature of the biomass at this point would generally be in the
range of 195.degree. to 200.degree. F. As mentioned previously, all
hydrogen peroxide should have been decomposed by the time the
biomass leaves the extruder. Additionally, the pH of the biomass at
this point will be in the area of 11.5.
Following reaction in the extruder 40, the substrate may be passed
via line 50 to cooling drum 52 where the substrate may be cooled
and dried. The product 54 may be utilized to feed ruminant
livestock, such as cattle and sheep. Alternatively, the product 54
may be converted into a chemical feedstock 58 by the addition of
appropriate fungal cellulose enzyme complexes, such as Trichederma
reesei, which is native to the ruminant's digestive system. The
addition of such enzymes converts the cellulose and hemicellulose
to glucose and xylose for the production of ethanol, acetic acid,
butanol and other chemical derivatives.
Alternatively, the extrudate from the reactor 40 may be processed
through a hydrolyzer 60, i.e., an agitated water tank having a
temperature of at least 140.degree. F. The purpose of the
hydrolyzer 60 is to wash out hemicellulose.
The product of the hydrolyzer 60 is then transferred via line 62 to
a filter 64 which filters out the hydrolyzer solution. The filter
64 acts in a similar fashion to the filter 20, previously
described. The product of the filter 64 can then be transferred via
line 66 to a conversion tank 68 in order to convert the product to
xylose or other chemical feed stocks in a manner similar to that
previously described with respect to the cooling drum 52.
Alternatively, the product of filter 64 should be washed at least
once and preferably at least two times in an acid bath 70. The
purpose of the acid bath is to wash out substantial amounts of the
lignin and hemicellulose remaining in the substrate. The pH of the
acid bath is reduced to 0.5 to 3 by adding hydrochloric acid from
storage tank 72 via line 74. Advantageously, the acid bath acts to
further bleach the cellulose fiber in the substrate in order to
make the final product brighter and whiter. Following multiple
washings in the acid bath 70, the substrate is transferred via line
76 to filter 78 which removes a substantial amount of the acid wash
solution. This acid wash solution may be recycled back to acid bath
70 via line 80.
The substrate is then transferred via line 82 to a subsequent
washing area 84, having a pH of 6.5 to 7.0. The pH is corrected by
the addition of buffering agents, such as calcium carbonate or
bicarbonate of soda from storage tank 86 via line 88. This washing
process affords a final removal of the bleaching or extraction
solutions and solublized compounds therein from the pulp prior to
recovery.
Following the pH correction process, the substrate is transferred
via line 90 to filter press 92. Filter press 92 is preferably a
hydraulic filter press, which reduces the moisture of the substrate
to a 55 to 65% moisture level. The liquid which is extracted from
the substrate may then be recycled via line 94 back to washer 84 in
order to reduce the cost of calcium carbonate and bicarbonate of
soda.
The compressed substrate from filter press 92 is then transferred
via line 96 to fluffer 100, which acts to break apart the condensed
hard packed substrate. The material is then transferred via line
102 to dryer 110, a fluid bed dryer, which dries the fluffed
material to a moisture content of approximately 3 to 8%. The
temperature in the fluid bed dryer 110 should not exceed
180.degree. F. in order to obtain the best coloring for the fiber
substrate.
Following drying, the substrate is passed via line 112 to a cutting
mill 120, which grounds the substrate fiber through preferably a 60
mesh screen with a cutting mill. Although other cutters, such as
hammer or ball mill types may be used, cutting mills are preferred.
This is because hammer and ball mills tend to compress the fluffy
cellulose and diminish the puffing or absorbing qualities of the
fiber.
The final product leaving the cutting mill 120 via line 122 enters
a powder tank 130 in preparation to be bagged at 132.
The entire system of the present invention may be hydraulically
controlled to maintain certain pressures, temperatures and
retention times, depending upon the substrate used, the amount of
water used and the amount of delignification desired. The whole
system can of course be computerized and controlled by pressures,
heat or end results and the capacity desired. The apparatus may be
powered by diesel power with water circulation through the diesel
engine block used as a boiler, along with the function which would
provide heat for cooking in the extruder. Excess hot water would
then be recycled to the water jacketed pre-pulper tank and then
back to the diesel motor block. Diesel would power the extruder and
hydraulic systems to control the orifice on the extruder.
The final product of the present invention preferably has a
particle size small enough to pass through a 100 mesh screen. Such
a particle is acceptable as a food grade material for total dietary
fiber. Additionally, this fiber has a brightness reading of over 80
GE units as measured by a General Electric brightness meter. The
dietary fiber is also a food product acceptable to the FDA residue
requirements.
Thus, the need for a nearly white, high percentage dietary fiber
can be met by applying the process of the present invention which
simultaneously delignifies, bleaches, shears, sterilizes and
liquifies the substrate causing both the lignin and hemicellulose
to be removed, leaving 80% or more cellulose in the final product.
The final product is a non-toxic, non-woody white fluffy cellulose
material which can be ground to a 120 mesh particle size and which
is highly soluble and non-gritty to the taste.
It is within the scope of the present invention to customize the
apparatus to leave in more lignin and hemicellulose or take out
more by simply changing the pH level during the process.
Additionally, the process may be mobilized as a portable unit,
which would effect tremendous savings on the cost of transporting
the substrate for livestock feeding.
The following examples are given to illustrate certain preferred
embodiments of the process of the present invention.
EXAMPLE 1
Example 1 is designed to illustrate the delignification of a
non-woody lignocellulose biomass substrate to a feed suitable for
ruminant digestion. The biomass substrate is chopped to a size not
exceeding 1/2 inch and forwarded to a prehydraulysis tank
containing water as a reaction medium. Potassium hydroxide is added
to the water to raise the pH to 11.5. The temperature of the water
is approximately 130.degree. F. The substrate is allowed to react
in this mixture for approximately 20 minutes. The substrate is then
pumped through a filter extractor to remove the lignin. The
reaction fluid is then recycled back to the prehydraulysis tank and
the substrate is conveyed to a mixer where the pH is converted to
11.5 and a chelating agent is added at a 2.5 to 4% v/v level. The
substrate is processed through the mixer for approximately 21/2
minutes at a pressure between approximately 300 and 400 psi and a
temperature of about 190.degree..
The substrate is then fed to an extruder reactor, and oxygen is
then introduced to create an oxygen atmosphere. Subsequently, a 10%
solution of hydrogen peroxide is introduced through a high pressure
orifice through a palladium gauze and into the reactor. The
hydrogen peroxide is added at a rate of 25 lbs. of hydrogen
peroxide per ton of substrate on a dry matter basis. After reacting
for approximately 45 to 60 seconds, the substrate emerges through a
hydraulically controlled valve in the extruder reactor. At this
point, the temperature of the substrate environment is between
approximately 200.degree. to 265.degree. F.
The substrate is then conveyed to a cooling drum where the
substrate is cooled and dried. The product of the cooling drum may
then be utilized to feed ruminant feed stock. Alternatively, the
product can be converted into a chemical feed stock by the
subsequent addition of appropriate enzymes.
EXAMPLE 2
Example 2 illustrates a preferred process for producing a dietary
fiber. The process according to Example 1 is followed through the
extruder reactor. Rather than forwarding the substrate to a cooling
drum, the substrate is hydrolyzed in an agitated vat in a pH
approximately 11.4 to 11.8 for approximately 30 minutes. The
substrate is then passed through a vibrating filter to separate the
substrate from the reaction fluid. The fluid may then be pumped
back to a recycle silo to concentrate the sugars and hemicellulose.
The substrate is then washed through an acid bath at a pH of 1.5.
After the acid bath, the acid is washed off and the pH of the
substrate is converted to at least 6.0. The acid bath may be
recycled back to the supply tank for further use. The product is
then hydraulically pressed to decrease the total moisture content
to the low 70%, followed by fluffing and drying in a fluid vat
dryer to bring the moisture to no more than 8%, preferably 4%. The
product is then forwarded to a cutting mill to cut the fibers to a
70 to 120 mesh size. The prepared dietary fiber may then be bagged
for transport.
EXAMPLE 3
Example 3 illustrates the process for the production of an
absorbent fiber for industrial purposes. The process of Example 2
is followed with the exception that the substrate leaving the
extruder reactor is hydrolyzed in an agitated vat having a pH
between 11.8 and 12.2. At this pH, most of the hemicellulose is
removed and only the cellulose remains in the substrate.
It is understood that the invention is not confined to the
particular construction and arrangement of parts herein illustrated
and described, but embraces such modified forms thereof as come
within the scope of the following claims.
* * * * *